1. Field of the Invention
The present invention relates to a clutch apparatus operable to engage and disengage transmission of a rotational drive power from a crankshaft of an engine to a transmission unit of a power unit. More particularly, the present invention relates to a twin clutch apparatus having a pair of clutches and a clutch outer member shared by the pair of clutches, a power unit incorporating same, and a vehicle incorporating same.
2. Description of the Background Art
There are a number of known clutch apparatus which are operable to engage and disengage transmission of a rotational drive power from an engine to a transmission unit of a power unit. Such known clutch apparatus generally include a friction plate and a clutch outer member.
The friction plate includes multiple protruding portions formed thereon. The protruding portions are arranged in the circumferential direction on the edge of the outer circumferential surface of the friction plate so as to protrude in a radial direction thereof.
The clutch outer member includes multiple groove portions formed therein. The multiple groove portions are arranged along the axial direction in an internal circumferential surface of the clutch outer member. The clutch outer member has a cylindrical shape having a closed bottom end.
The protruding portions of the friction plate are engaged with respective groove portions of the clutch outer member with a clearance between each protruding portion and groove portion. Accordingly, the friction plate is engaged with the clutch outer member, and the friction plate is allowed to move in the axial direction, but is not allowed to rotate independently of the clutch outer member.
An example of such known clutch apparatus is disclosed in the Japanese Patent Application Publication No. H07-238951, which discloses a single clutch apparatus. However, the Japanese Patent Application Publication No. H07-238951 does not disclose a twin clutch apparatus having a pair of clutches, as proposed by the present invention.
Further, in an ordinary twin clutch apparatus, a demand for reducing the number of component, parts, mainly requires that the pair of clutches share a single, common clutch outer member. As a result, when a single, common clutch outer member is shared by a pair of clutches, length of the clutch outer member in the axial direction increases, and so do the lengths of the groove portions formed in the clutch outer member.
When such a clutch outer member having an elongated longitudinal dimension (length) in the axial direction is fabricated, additional measures are required to facilitate pulling out of the core for forming the groove portion in the clutch outer member. Each of the groove portions is formed in a tapered shape with a radial width thereof gradually increasing towards an open-end side of the clutch outer member.
However, the tapered shape of the groove portion formed in the clutch outer member having a radial width thereof gradually increasing, as described above, forms a clearance between the groove portion of the clutch outer member and the protruding portion of the friction plate which increases towards the open-end side of the clutch outer member.
As a result, the groove portion near the open-end side of the clutch outer member has the largest clearance. This would cause little problem, if any, if a clutch apparatus has a short length in the axial direction, such as the single-clutch apparatus disclosed in the Japanese Patent Application Publication No. H07-238951.
However, when a twin clutch apparatus having a single, commonly shared clutch outer member, the clearance between the groove portion of the clutch outer member and the protruding portion of one of the pair of clutches that is placed towards the open-end side increases because of the increased length of the clutch outer member in the axial direction. As a result, both undesirable force and sound caused by the impact between the clutch outer member and the friction plate is increased.
The present invention has been made to overcome such drawbacks. Accordingly, it is an object of the present invention is to provide a twin clutch apparatus that is operable to control a clearance between the groove portion of the clutch outer member and the protruding portion of the friction plate within an appropriate, desirable range, even when the width of the groove portion of the clutch outer member is increased. It is also an object of the present invention to provide the twin clutch apparatus which reduces force and sound caused by the impact during operation between the clutch outer member and the friction plate.